mouth outward the mucous membrane of the cheek can be inspected, and on this, opposite the second molar tooth of the maxilla, is the little papilla which marks the orifice of the parotid duct.

In the floor of the mouth is the tongue(Fig. 1201). Its upper surface is convex and is marked along the middle line by a shallow sulcus; the anterior two-thirds are rough and studded with papillæ; the posterior third is smooth and tuberculated. The division between the anterior two-thirds and the posterior third is marked by a V-shaped furrow, the sulcus terminalis, which is situated immediately behind the line of the vallate papillæ.

FIG. 1202 The mouth cavity. The apex of the tongue is turned upward, and on the right side a superficial dissection of its under surface has been made. (See enlarged image)

On the under surface of the tongue (Fig. 1202) the mucous membrane is smooth and devoid of papillæ. In the middle line, the mucous membrane extends to the floor of the mouth as a distinct foldthe frenulumthe free edge of which runs forward to the symphysis menti. Sometimes the ranine vein can be seen immediately beneath the mucous membrane, a little lateral to the frenulum. Close to the attachment of the frenulum to the floor of the mouth, the slit-like orifice of the submaxillary duct is visible on either side. Running backward and lateralward from the orifice of the submaxillary duct is the plica sublingualis, produced by the projection of the sublingual gland which lies immediately beneath the mucous membrane. The plica serves also to indicate the line of the submaxillary duct and of the lingual nerve. At the back of the mouth is the isthmus faucium, bounded above by the palatine velum, from the free margin of which the uvula projects downward in the middle line. On either side of the isthmus are the two palatine arches, the anterior formed by the Glossopalatinus and the posterior by the Pharyngopalatinus.